Chemical reduction nickel plating bath



nited States Patent CHEMICAL REDUCTION NICKEL PLATING BATH Lawrence V.Puls, Ferndale, and William R. Vincent,

Birmingham, Mich., assignors to General Motors Corporation, Detroit,Mich., a corporation of Delaware No Drawing. Application February '10,1958 Serial No. 714,077

13 Claims. (Cl. 117'130) This invention relates to an improved bath andprocess for nickel plating by chemical reduction.

It is well known that various metals may be nickel plated by chemicalreduction in an aqueous bath containing nickel ion and hypophosphiteion, the plating reaction being:

This reaction whereby the plating occurs is catalytic and autocatalytic,its initiation usually being accomplished by way of the catalytic effectof the article being plated and its continuance being catalyzed by thenickel which is deposited. Various metals may be plated by the process,for example, copper, gold, aluminum, iron, nickel, silver, cobalt,palladium, platinum. Magnesium and thorium also display the catalyticeffect and theoretically, therefore, may be plated by the process;however, the plating of these metals has presented a serious problem inthat when they are immersed in baths such as have heretofore been used,they are chemically attacked by the solution with the result that asatisfactory plate is not obtained.

It is an object of the present invention to provide an improvedelectroless nickel plating bath and process which is particularly usefulfor nickel plating magnesium and also thorium. Another object of theinvention is the provision of an electroless nickel plating bath andprocess which provides an improved nickel deposition and which hasimproved stability even in the presence of magnesium and thorium. Whilethe bath and process have particular utility and advantages in theplating of magnesium and thorium, other metals such as those mentionedabove may also be plated, the improved stability and the high platingrate of the bath and process being highly advantageous irrespective ofthe precise metal being plated. Other objects and advantages of theinvention will appear more fully from the following description ofvarious embodiments thereof.

In accordance with the invention the aqueous nickel plating bath isformulated to contain the following ingredients in the concentrationindicated:

Nickel ion From .005 to .20 mole per liter. Hypophosphite ion From .01to .40 mole per liter. Fluoride ion From .20 to 1.0 mole per liter.

Alkyl or alkanol amine Sufficient to provide an N to Ni++ ratio of from1:1 to :1.

Carboxylie acid or salt thereof as a Suifieient; to produce a carboxylbuffer. group-toypophosphite ion ratio from 1:1 to 10:1. Initial pH 7 to11.

amples, the carboxylic acid used as the buffer may be a polycarboxylicacid or an hydroxy carboxylic acid. Sincea polycarboxylic acid furnishesmore carboxyl groups per mole than, does a monocarboxylic acid, theiruse is generally desirable. We prefer to use citric acid as the buffer.

The amine must be sutficiently soluble in the bath to provide thedesired concentration, and must also have a sufficiently high boilingpoint so that it is not lost due to evaporation at the desired bathtemperature which should be in the range of F. to 210 F., preferablyabove F. Amines which are satisfactory are any of the primary, secondaryor tertiary ethyl amines or propyl amines, ethylene or propylene'diamine, ethanol amine, di or tri ethanol amine, methanol amine, diortri methanol amine, propanol amine, or di or tri propanol amine.

The initial pH of the bath, which is on the alkaline side, may beadjusted-by addition of the amine ingredient or by the addition ofsodium or potassium hydroxide. For optimum results, however, it ispreferred that the N to N ratio be on the order of 5:1 and thus it isdesirable to add just suflicient amine to provide this preferred ratioand then adjust the initial pH by the addition of potassium hydroxide orsodium hydroxide.

The following specific examples will serve to illustrate, Example Ibeing the preferred bath by way of its precise ingredients and also byway of the amounts thereof which are used:

Example I Nickel sulfate -grams per liter.- 5.5 Sodium hypophosphite--do-- 8.3 Citric acid (in 10 Triethanolamine N(C H OH) -ml. perliter... 20 Ammonium bifluoride (NH F-HF) grams per liter 10 pH(adjusted by addition of NaOH) 8.0 Temperature F-. 205

Example II Nickel sulfate "grams per liter 5 Sodium hypophosphite do----8. Acetic acid do- 10 Triethanolamine --ml. per liter Approx. 60Ammonium bifluoride -grams per liter.- 10 pH (adjusted by the amineadded) 8.0 Temperature F..- 190 Example III Nickel sulfate grams perliter..- 5.5 Sodium hypophosphite ..do..... 83 Citric acid dn 9Potassium fluoride do 11.8 Ethanolamine NH (C H OH) -ml. per liter-- pH(adjusted by addition of KOH) 8-0 Temperature F -190 Example IV Nickelsulfate grams per liter 11 Sodium hypophosphite do 16.6 Citric acid dn17 Potassium fluoride do 21.7 Triethanolamine mls. per liter..- 40 pH(adjusted with KOH) 8.1 Temperature F 185-190 Example V Nickel sulfate"grams per liter-- 5 Sodium hypophosphite do 8.3 Citric acid do- 8Ammonium bifluoride do.. 8 Triethylamine N(C H --mls. per liter--Approx. 80 pH (adjusted by the amine added) 10.85 Temperature F... 210

To practice the process of the invention, the magnesi- ;ll ,1- thn m. orother metalarticle to be plated :is first t roughly .cleaned byconventional degreasing and chemical. cleaning procedures and .is thenimmersed. into the bath until the desired :plating. thickness isobtained.

The. precise plating. rate attained is dependentupon the concentrations.of -thefbath :ingredients and also upon hathtemperature. :Ingeneral,.the' higher the nickel in concentration .and the higher thetemperature, thefaster the:plating ratmkhowever =with increased nickelconcentration =and- ;with increased: temperature the greater is thepossibility-of bath instability. The preferred bath as set forth inExampleI-provides an initial plating rate ofabout .0015 inch per hour.which is excellent; at the same time, this bathis verystableand cantherefore be operated on a production basis-without the hazardofprecipitation occurring.

After the bath hasbeen operated -for-a time it may, if desired,be'replenished 'bythe addition-of nickel ion, -hypophosphite ion andpotassium or sodium hydroxide. For example a bath as specified inExample V above was operated untilthere was substantial depletion of thenickel ion (at which point the pH of the bath was 6.4) and thenreplenished by the addition of 9 grams nickel sulfate,,9 .grams sodiumhyphosphite and suflicient sodium hydroxide to raise .the pH to 10.9.The replenished bath wasjhen ,used again for furtherplating until thenickel was once more. depleted. Also, replenishment may, if desired, beon acontinuous basis so as to keep the bath-in continuous operation foran extended period.

It is to be nnderstoodthat while the-inventionhas been described chieflyby reference to particular embodiments thereof, it is not so limitedsince various changes and modifications may be made, all within the fulland intended scope of the claims which follow.

We-claim:

1. Achemicalreduction type-nickelplating bath comprisingranaqueous-solution having an initial pH of between 7-and 11 and containingthe following in the concentrations indicated:

Nickel ion From .005 to .20 mole per liter. Hypophosphite ion... From.01 to .40 mole per liter. Fluoride ion From .20 to 1.0 mole per liter.Alkyl or alkanol amine .-Suflicient to provide an N to Ni++ ratio 01from 1:1to 10:1. Cajrlbggrylic acid or salt thereof as a Sufiicicnt toproduce .a carboxyl group-to-hypophosphite ion ratio of from 1:1.tol0:1.

2. A chemical reduction type nickelplating bath comprising anaqueous-solutionhavingan initial pH of between 7 and lland containingfrom-.005 to .20 mole per liter nickel ion, from .01 to .40 mole-perliter hypophosphite ion, from .20 to 1.0 mole per liter fluoride ion,sutficient amine to provide an N to Ni++ ratio of from 1:1 to 10:1 andsufiicient carboxylic acid'bufier to produce a carboxylgrOUp-to-hypophosphite ion ratio of'from 1:1 to 10:1, said aminebeingselected from the group consisting of the methyl, ethyl and propylamines, the methanol, ethanol and propanol amines and the ethylene andpropylene diamines.

3. A chemical reduction type-nickel plating bath comprising an aqueous.solution having an initial pH of between 7 and 11 and containing from.005 to .20-m ole per liter nickel ion, from .01 to .40 mole per literhypo- ;phosphite ion, from .20 to 1.0 mole per liter fluoride ion,sufficient amine to provide an N to Ni++ ratio of from ;1:1.to 10:1 andsuflicient carboxylic acid buffer to pro- 4 duce a carboxylgroup-to-hypophosphite ion ratio of from 1:1 to 10:1, said ,amine beingselected from the group consisting of the methyl, ethyl and propylamines, the methanol, ethanol and propanol amines and the ethylene andpropylene diamines, and said butter being selected from the groupconsisting of acetic acid, propionic acid, succinic acid, lactic acid,glycolic acid, citric acid and the soluble saltsthereof.

4. A hemical reduction type nickel plating bath comprising an aqueoussolution having an initial pH of between 7 and 11 and containing nickelsulfate sufficient to produce from .005 to .20 mole per liter nickelion, sodium hypophosphite sufiicient to produce from .01 to .40 mole perliter hypophosphite tion, ammonium bifiuoride sufficient to produce from.20 to 1.0 mole per liter fluoride ion, triethanolamine sufficient toprovide an N to Ni++ ratio of from 1:1 to 10:1 and citric acidsufficient to produce a carboxyl group-to-hypophosphite ion ratio ofirom1:1 to 10:1.

5. A chemicalreduction type tnickel plating bath comprising an aqueoussolution having an initial pH of between 7 and 11 and containing the.following in the concentrations indicated:

Nickel ion From .005 to .20 mole per liter. Hypophosphlte ion From .01to .40 mole per liter. Fluoride ion From .20 to 1.0 mole per liter.Alkyl or elkanol amin Sufficient to provide an N to N ratio of about5:1. Cerboxylic acid or salt thereof as a Sufficient to produce acarboxyl buiier. group-to-hypophosphite ion ratio of from 1:1 to 10:1.

6. Achemical reduction type nickel plating bath comprising an aqueoussolution having an initial pH of about 8 and containing the following-inthe concentrationsindicated:

Nickel sulfate grams per liter-.. 5.5 Sodium hypophosphite do 8.3 Citricacid do 10 Triethanolamine ml. per liter 20 Ammonium bifluoride gramsper liter 10 7. A process for depositing nickel by chemical reductioncomprising immersing the article to be plated in a bath maintained at atemperature of between and 210 F., having an initial pH of between 7 and11 and containing the following in the'concentrations indicated:

Nickel ion From .005 to .20 mole per liter. Hypophosphite ion From .01to .40 mole per liter. Fluoride ion From .20 to 1.0 mole per liter.Alkyl or alkanol amine Sufficient to provide an N to Ni- Nickel ionHypophosphite ion From .01 to .40 mole per liter Fluoride ion From .20to 1.0 mole per liter. Alkyl or alkanol amine.-. Sufficient to providean N' to Ni++ ratio of from 1:1 to 10:1. Carboxylic acid or salt thereofas a Sufiicient to produce a carboxyl er. group-to-liypopliosphite ionratio of from 1:1 to 10:1. 9. A process for nickel plating by chemicalreduction an article made of a metal selected from the group consistingof magnesium and thorium, said process comprising immersing said articlein a solution having an initial pH of between 7 and 11 and containingfrom .005 to .20 mole per liter nickel ion, .from .01 to .40 mole perliter hypophosphite ion, from .20 to 1.0 mole per liter fluoride ion,suflicient amine to provide. an N to Ni++ ratio of from 1:1 to 10:1 andsufficient carboxylic acid buffer to producea carboxylgrouprto-hypophosphite ion ratio of-from 1:1 to 10:1, said amine beingselected from the group consisting of the methyl, ethyl and propylamines,

the methanol, ethanol and propanol amines and the ethylene and propylenediamines.

10. A process for nickel plating by chemical reduction an article madeof a metal selected from the group consisting of magnesium and thorium,said process comprising immersing said article in a solution having aninitial pH of between 7 and 11 and containing from .005 to .20 mole perliter nickel ion, from .01 to .40 mole per liter hypophosphite ion, from.2 to 1.0 mole per liter fluoride ion, suflicient amine to provide an Nto Ni++ ratio of from 1:1 to 10:1 and sufiicient carboxylic acid buiferto produce a carboxyl group-to-hypophosphite ion ratio of from 1:1 to10:1, said amine being selected from the group consisting of the methyl,ethyl and propyl amines, the methanol, ethanol and propanol amines andthe ethylene and propylene diamines, and said buffer being selected fromthe group consisting of acetic acid, propionic acid, succinic acid,lactic acid, glycolic acid, citric acid and the soluble salts thereof.

11. A process for nickel plating by chemical reduction an article madeof a metal selected from the group consisting of magnesium and thorium,said process comprising immersing said article in a solution having aninitial pH of between 7 and 11 and containing nickel sulfate sufiicientto produce from .005 to .20 mole per liter nickel ion, sodiumhypophosphite suflicient to produce from .01 to .40 mole per literhypophosphite ion, ammonium bifiuoride suflicient to produce from .2 to1.0 mole per liter fluoride ion, triethanolamine sufficient to providean N to Ni++ ratio of from 1:1 to 10:1 and citric acid sufiicient toproduce a carboxyl group-to-hypophosphite ion ratio of from 1:1 to 10:1.

12. A process for nickel plating by chemical reduction an article madeof a metal selected from the group consisting of magnesium and thorium,said process comprising immersing said article in a solution having aninitial pH of between 7 and 11 and containing the following in theconcentrations indicated:

Nickel ion From .005 to .20 mole per liter. Hypophosphite ion From .01to .40 mole per liter. Fluoride ion From .2 to 1.0 mole per liter.

Nickel sulfate "grams per liter 5.5 Sodium hypophosphite do 8.3 Citricacid do 10 Triethanolamine ml. per liter 20 Ammonium bifluoride gramsper liter 10 References Cited in the file of this patent UNITED STATESPATENTS 2,694,017 Reschan et a1. Nov. 9, 1954 2,694,019 Gutzeit Nov. 9,1954 2,772,183 Talmey et a1. Nov. 27, 1956

1. A CHEMICAL REDUCTION TYPE NICKEL PLATING BATH COMPRISING AN AQUEOUSSOLUTION HAVING AN INITIAL PH OF BETWEEN 7 AND 11 AND CONTAINING THEFOLLOWING IN THE CONCENTRATIONS INDICATED: